Pen Djeco of type rollerball, with blue ink. Rollerball pens have a writing similar to that of a fountain pen. They produce the most ink compared to other types, have comfortable writing, do not skip, but may smudge. Not recommended for low-quality paper and left-handed individuals. The ink lasts less compared to ballpoint and gel types. It has invisible ink that is not visible during writing but becomes visible when illuminated, usually with a specific light.